Ancylus, from Lake Ochrid, Macedonia. The shell apex provides especially useful diagnostic characters in the Ancylidae, especially at the generic level. But there are sometimes obvious differences between species of the same genus. Shown here are the shell apices of two Lake Ochrid Ancylus species.
John B. Burch (photographer; copyright holder), Mollusk Division, Museum of Zoology, University of Michigan-Ann Arbor